Characters in Friends didn't have 85 total sex partners. I have way too much time: the total is 138-ish.

I know every Friend episode by heart. I watched each and every one of them more than once to come up with this total, which includes past sex partners that are just mentioned. Detailed Excel spreadsheet and everything. I wish someone would do a graphic representation of this. (Here is the only graph I attempted.)

In episode 22 of Season 2 ("The One with the Two Parties"), Joey took the lead in sex partner count and there was no way back.

Joey and Ross have taken part in threesomes. (EDIT: As several redditors pointed out, Ross' threesome wasn't really real. The other woman taking part (Susan) wasn't included in Ross' stats, so the numbers are fine. No worries. Thankfully, the universe isn't going to implode.)

Season 6 was definitely the quietest sex-wise. Only 4.5 new sex partners are discovered.

During Season 1, Monica is the most promiscuous character (with 9.5 sex partners discovered). In Season 3 Joey breaks this record, with 10.5 new sex partners discovered.

Chandler holds the record for LESS new partners discovered continuously. After having sex with Monica (end of Season 4), no new sex partners are discovered until the end of the series (i.e., 6 seasons with no new sex partners mentioned.) Regarding Monica, we discover in episode 11 of Season 7 ("The One with All the Cheesecakes") that she had had sex with Stuart, her cousin's new husband.

TL;DR: I've carried out a profound study on Friends' sex life and sharing some info makes me feel less of a moron.

EDIT: Wow, what a beautiful response. I have now uploaded my Excel spreadsheet with all the details. Click here to download (I couldn't find any other better/quicker way to share it.) It includes the name, episode of first mention and comments of each sex partner of each Friend (quite organized, of course. Comment cells in grey indicate "unconfirmed sex" (or "half sex", the term I used in the spreadsheet). The second tab or sheet (named "stats per season" is exactly that: a summary of the data but in numeric form, per season. It includes the graph, of course.

Enjoy!

EDIT 2: Well, this post has been featured in several media outlets, which is pretty cool.

Finally, click on your username at the top right corner of reddit, click on comments, and click on the new OVERWRITE button at the top of the page. You may need to scroll down to multiple comment pages if you have commented a lot.